Cubic boron nitride/sintered carbide abrasive bodies

ABSTRACT

Abrasive bodies comprising combinations of cubic boron nitride crystals and sintered carbide are disclosed. These composite bodies are prepared by superpressure processes. Cubic boron nitride contents of up to about 99 volume percent have been successfully employed in certain constructions. Similar abrasive bodies have been prepared from mixtures of cubic boron nitride, diamond and carbide powder.

United States Patent Wentorf, Jr. et al.

[ 1 *Oct. 23, 1973 CUBIC BORON NlTRlDE/SlNTERED CARBIDE ABRASIVE BODIESlnventors: Robert H. Wentorf, Jr.,

Schenectady; William A. Rocco, Scotia, both of N.Y.

Assignee: General Electric Company,

Schenectady, N.Y.

Notice: The portion of the term of this patent subsequent to July 3,1990, has been disclaimed.

Filed: July 1, 1971 Appl. No.: 158,709

U.S. Cl 51/307, 51/309, 264/65 Int. CL... B24d 7/14 Field of Search51/293, 307, 308,

References Cited UNITED STATES PATENTS 2/1966 Wentorf et al 51/3092,888,355 5/1959 Taylor 51/307 3,136,615 6/1964 Bovenkerk et a1 51/3093,192,015 6/1965 Wentorf 51/307 3,212,851 10/1965 Bundy et al.... 51/3072,947,617 8/1960 Wentorf 51/307 Primary ExaminerDonald J. ArnoldAtt0rneyJohn F. Ahern et al.

57 ABSTRACT Abrasive bodies comprising combinations of cubic boronnitride crystals and sintered carbide are disclosed. These compositebodies are prepared by superpressure processes. Cubic boron nitridecontents of up to about 99 volume percent have been successfullyemployed in certain constructions. Similar abrasive bodies have beenprepared from mixtures of cubic boron nitride, diamond and carbidepowder.

15 Claims, 7 Drawing Figures mmmnmz m 3.76713 71 m z lgz.

fr? ventor-as: Robert H. Wentorfd William A. Rocco,

heir A ttor'n ey.

CUBIC BORON NITRIDE/SINTERED CARBIDE ABRASIVE BODIES BACKGROUND OF THEINVENTION The preparation of cubic boron nitride (CBN) is disclosed andclaimed in U. S. Pat. No. 2,947,617 Wentorf. The bonding together of CBNcrystals to form a compact abrasive body is disclosed in each of U. S.Pat. No. 3,136,615 Bovenkerk et al. and U. S. Pat. No. 3,233,988 Wentorfet al. Each of the aforementioned patents is incorporated by reference.

The production of ever more dense, tougher compacts of CBN is constantlybeing sought in order to improve the capabilities for machiningnickel-base superalloys at higher speeds, e.g., at greater than 50surface feet/minute.

SUMMARY OF THE INVENTION Superpressure processes have been employed toprepare abrasive compacts comprising combinations of CBN crystals andsintered carbide. Good compacts have been produced employing CBNcrystals greater than about 80 micrometers in largest dimension.

Combinations of CBN crystals, carbide powder and diamond crystals havealso been successfully employed to prepare useful compacts. Compositebodies in which a layer of CBN crystals has been bonded to the surfaceof a sintered carbide disc have been prepared in which the CBN layer hasbeen found to be essentially free of voids.

BRIEF DESCRIPTION OF THE DRAWING This invention will be betterunderstood from the following description and drawing in which:

FIG. 1 illustrates on exemplary high pressure, high temperatureapparatus useful in the preparation of the product of this invention;

FIG. 2 illustrates in section one form of a charge assemblyconfiguration for use within the apparatus of FIG. 1 in the practice ofthe instant invention;

FIG. 3 is a three-dimensional view illustrating a composite CBN machinetool insert;

FIG. 4 is a section taken through the insert of FIG. 3 either on line XXor on line YY;

FIGS. 5 and 6 are each three-dimensional views of composite CBN/sinteredcarbide machine tool inserts prepared according to this invention andFIG. 7 is a sectional view showing a combined liner/- charge assemblyfor preparing the structures of FIGS. 3, 5 and6.

DESCRIPTION OF THE PREFERRED EMBODIMENT One preferred form of a highpressure, high temperature apparatus in which the composite tool insertof the instant invention may be prepared is the subject of U. S. Pat.No. 2,941,248 Hall (incorporated by reference) and is brieflyillustrated in FIG. 1. Reaction vessel arrangements useful in thepractice of this invention are described in u. s. Pat. application S.N.144 Wentorf, Jr. (now U. S. Pat. No. 3,609,818), filed Jan. 2, 1970(incorporated by reference).

Apparatus 10 includes a pair of cemented tungsten carbide punches 11 and1 l and an intermediate belt or die member 12 of the same material. Diemember 12 includes an aperture 13 in which there is positioned areaction vessel 14. Between punch 11 and die 12 and between punch 11'and die 12 there are included gasket/insulating assemblies l5, 15, eachcomprising a pair of thermally insulating and electrically nonconductingpyrophyllite members 16 and 17 and an intermediate metallic gasket 18.

Reaction vessel 14 in one preferred form, includes a hollow saltcylinder 19. Cylinder 19 may be of other material, such as talc, whicha). is not converted during high pressure-high temperature operation toa stronger, stiffer state (as by phase transformation and or compaction)and b). is substantially free of volume discontinuities occurring underthe application of high temperatures and pressures, as occurs, forexample, with pyrophyllite and porous alumina. Materials meeting thecriteria set forth in U. S. 3,030,662 Strong (column 1, lines 59 throughcolumn 2, line 2, incorporated by reference) are useful for preparingcylinder 19.

Positioned concentrically within and adjacent cylinder 19 is a graphiteelectrical resistance heater tube 20. Within graphite heater tube 20there is in turn concentrically positioned the cylindrical salt liner21. The ends of liner 21 are fitted with salt plugs 22, 22', disposed atthe top and bottom, respectively. As will be described hereinbelow liner21 may have a cylindrical. hollow core to receive one large chargeassembly containing sub-assemblies or the liner may consist of a seriesof mold assemblies arranged in a stack for the preparation of aplurality of composite tool inserts, e.g., as shown in FIGS. 3, 5, and6.

Electrically conductive metal end discs 23 and 23' are utilized at eachend of cylinder 19 to provide electrical connection to graphite heatertube 20. Adjacent each disc 23, 23 is an end cap assembly 24 and 24'each of which comprises a pyrophyllite plug'or disc 25 surrounded by anelectrically conducting ring 26.

Operational techniques for simultaneously applying both high pressuresand high temperatures in this apparatus are well known to those skilledin the superpressure art. The foregoing description relates to merelyone high pressure, high temperature apparatus. Various other apparatusesare capable of providing the required pressures and temperatures thatmay be employed within the scope of this invention.

FIG. 2 illustrates an arrangement for producing a plurality of disc-orpill-shaped conposites (sintered car bide substrate with a layer ofsintered CBN formed thereover). Charge assembly 30, although notillustrated to the same scale, fits within space 31 of the apparatus ofFIG. 1.

Charge assembly 30 consists of cylindrical sleeve-32 of shield metalselected from the group consisting of zirconium, titanium, tantalum,tungsten and molybdenum. Within cylindrical shield metal sleeve 32 aredisposed a number of sub-assemblies protected above and below byshielding discs 33 made of a metal selected from the group enumeratedfor the prepartion of sleeve 32 except as stated hereinbelow. Eachsub-assembly so protected on all sides consists of larger mass 34 andsmaller mass 36. Each mass 36 is largely or completely made up of CBNpowder (greater than about micrometers in largest dimension).

By employing a pre-sintered carbide disc for mass 34 and clean CBNcrystals larger than about mesh (U. S. Sieve) size for mass 36, withoutfurther additives, a single abrasive body may be produced as describedbelow in which the CBN portion is essentially free of voids and isaffixed to the carbide disc by excellent bonding.

EXAMPLE I Essentially pure CBN grit, 100 mesh size, was distributed in amass over one face of a hard sintered carbide disc made from grade 883Carboloy carbide powder. The combination was enclosed in a thinzirconium shield to exclude and remove oxygen. This assembly wassurrounded in turn by NaCl elements (to fill volume 31) in a highpressure apparatus. After about an hour under the application of highpressure and high temperature (55-60 kb and 1,500C) a composite abrasivebody was recovered. The cubic boron nitride portion was found to beessentially free of voids and an excellent bond was found to existbetween the sintered carbide and adjacent CBN.

The composite of Example I was examined and it was found that thesubstantial elimination of voids in the CBN mass (99 volume percent CBN)had been achieved by several mechanisms:

a. the intrusion of zirconium metal (from the sheath) to a small depth,e.g., 0.2 mm;

b. crushing of the CBN grains (which then can consolidate);

c. the intrusion of carbide material between CBN grains during the hightemperature treatment when the carbide material was in the plasticstate) and d. direct bonding between CBN grains.

The CBN grains had large areas of contact with each other and appearedto have been partly plastically deformed to accommodate each other.

In order to retain the benefits of mechanically unstable structuring ofthe charge assembly, discs 37 are made of the same material as cylinder19, e.g., NaCl, hexagonal BN to provide necessary follow through actionto occupy reduced volume within each subassembly during the process.

Sinterable carbide powder as described hereinbelow may be used in placeof the pre-sintered carbide as mass 34. In such a case sintering of thecarbide powder occurs in situ.

The direct bonding relationship created between the very high strengthCBN material and the significantly larger mass of underlying stiffcarbide support material obviates any need for the interposition of anybonding layer therebetween, as for example results from brazing orsoldering. By providing stiff, non-yielding support material in directcontact with the CBN-rich machining edge region, the incidence offractures in the CBN material during use of the tool insert in machiningis minimized.

Composites prepared in accordance with this invention have at times beenaccidentally broken during decompression of the reaction vessel torecover the product. This type of breakage occurs in a directiongenerally perpendicular to the vertical axis of the charge assembly. Inthe case of the composites produced with the sub-assemblies of FIG. 2the interface between the CBN and the sintered carbide lies in this samedirection. The high quality of the bond at this interface is shown bythe fact that most usually the breakage occurred through the CBN layer.Only rarely did breakage occur at the interface and in these instancesthe breakage surface was irregular, passing through the CBN and throughthe sintered carbide as well as along the interface. Thus, the interfaceis in general stronger than the tensile strength of the CBN crystals.

Microscopic (300X) examination of the polished edges of compositesshaped into tool inserts has shown the reasons for this unusually stronginterface bond. In good bonding" the CBN grains at the interface appear(at 300X magnification) either to be in direct contact with the sinteredcarbide or to have a thin reaction layer disposed between the CBN grainsand the sintered carbide. Any reaction layer is less than 10 micrometersthick indicating that in any case minimal disruption of, and attack on,the sintered carbide structure occurs. The interface is free of voidsand is irregular on the scale of micrometers ll0O/.L) due to pushing ofthe CBN into the sintered carbide and/or because of the movement ofplastically deformed sintered carbide into interstices between adjacentCBN crystals. This type and quality of interlocked interface is clearlyunattainable by soldering of a pre-formed CBN compact to a sinteredcarbide disc.

The preparation of CBN compacts for use as the abrading elements incutting and grinding tools is disclosed in the aforementioned Wentorf,Jr. et al. and Bovenkerk et al. patents. After preparation, the compactprepared therein is attached to some support. There is no teaching inthese patents leading the technician to the preparation of a compositetool insert in which a CBN compact when formed is simultaneouslyintegrated with a sintered carbide support mass as in the instantinvention in any way and, in particular, without the use of additivematerials.

ln addition to the type of composite body described hereinabove in whicha mass of CBN crystals are supported on and bonded to a pre-formedsintered carbide mass, two other types of composites may be prepared.Both of the latter composites embody a relatively uniform distributionof sintered carbide in a mass of abrasive grains. In the second type ofcomposite the abrasive grains are CBN grains while in the third type ofcomposite the abrasive grains are a mixture of CBN grains and diamondgrains.

EXAMPLE II A mixture of 94 percent by volume CBN grit and 6 percent byvolume Carboloy grade 883 carbide powder (6 percent Co, 94 percent WC)was enclosed in a thin Zr shield (to exclude and remove oxygen). Thisassembly was introduced into a high pressure, high temperature apparatusas described in Example I. The mixture was subjected to about 55 kb and1500C for about 60 minutes. Microscopic examination of polished surfacesof the resulting composite shows that the sintered carbide had movedinto the most minute crevices between CBN grains. Although directbonding between CBN grains was not extensive in this type of composite,the bond between CBN and metal (carbide) was excellent. A fracturedsurface of the composite displayed very few sites at which a CBN grainhad been pulled out of the system. Instead, the CBN grain had fractured.No reaction layer was observed next to the CBN grains at 300Xmagnification.

For the preparation of this type of composite, preferably, CBN crystalcontents of from about volume percent to about 94 volume percent areused. With this large CBN content, direct contact occurs between CBNcrystals under the high pressures employed. As a result, crushing ofgrains occurs and a large fraction of the initial void space becomesfilled by fragmented CBN grains. Intruding carbide powder apparentlyhinders direct bonding between CBN grains, but CBN/carbide bondingprovides a tough, strong, abrasive body.

CBN grain contents of less than 70 volume percent may, of course, beused. Sintering times may vary from about to about 60 minutes. Pressuresranging from about 45 to 60 kb may be used. Temperatures employed mayvary from l,300 to 1,600C. Combinations of pressure and temperatureshould be selected which will insure thermodynamic stability of the CBN.

This second type of composite may, in turn, be bonded to a sinteredcarbide support block by conventional means, e.g., solders. As analternate, this composite/support block structure may be prepared insitu a). by disposing the CBN grit/carbide powder mixture over thesurface of a sintered carbide disc or b). by using in combination alayer of sinterable carbide powder and contiguous therewith, a layer ofCBN grit/carbide powder mixture. In these alternate arrangements, as inthe arrangements previously described, the reaction mass is preferablycontained in a zirconium sheath.

The carbide powder, where employed, is preferably a tungsten carbidemolding powder (mixture of carbide powder and cobalt powder)commercially available in particle sizes of from 1 to 5 microns. Thetungsten carbide may, if desired, be replaced in whole or in part byeither or both of titanium carbide and tantalum carbide. Since some useof nickel and iron has been made in the bonding of carbides, thematerial for providing the metal bond in the cemented carbide may beselected from the group consisting of cobalt, nickel, iron and mixturethereof. Cobalt, however, is preferred as the metal bond material. Thecomposition of carbide molding powders useful in the practice of thisinvention may consist of mixtures containing about 75-97 percent carbideand about 3-25 percent metal bond material. Examples of carbide powdersused are Carboloy grade 883 carbide (6 percent Co, 94 percent WC) andCarboloy grade 905 (3 percent Co, 93 percent WC, 3.85 percent TaC, 0.15percent TiC).

For the preparation of the third type of composite (CBN grains, diamondgrains and sintered carbide) the description set forth hereinabove forthe preparation of the second type of compact is applicable except forthe abrasive grain content. Because of the diamond content, disc 33should be either zirconium or titanium. Mixtures of CBN and'diamondabrasive grains may range from 1 volume percent CBN and 99 volumepercent diamond to 99.volume percent CBN and 1 volume percent diamond.Pressures, temperatures and sintering times are comparable with thoseused in the preparation of the second type of composite, except that thethermodynamic stability of diamond, that is present, requires slightlyhigherpressures and/or lower temperatures than in the second type ofcomposite.

EXAMPLE III A unit comparable to one sub-assembly in FIG. 2 was preparedin a Zr container (0.250 inch diameter). The charge therefor consistedof a disc of 883 grade Carboloy sintered carbide (0.121 inch thick) and,in conposite produced was polished into a cutting tool and tested bycutting Rene 41 superalloy on a lathe. The tool cut the superalloy, butthe diamond portion of the abrasive compact wore away too quickly.Microscopic examination established that good diamond/diamond bondinghad been accomplished during manufacture and there was good bonding bythe diamond and CBN grains to the carbide support. Occasional CBN/CBNbonding but no diamond/CBN bonding was observed.

Referring now to the composite tool inserts shown in FIGS. 3, 5, and 6,in the preparation of any of these non-cylindrical shapes, a modifiedconstruction of salt liner 21 and plugs 22, 22 is required. Thus, thestructure fitting within heater tube 20 may be formed as a series ofcylindrical blocks in stacked cooperating arrangement to provide moldsto be filled with the constituents, e.g., mixture of carbide moldingpowder and CBN grains. By way of example, in FIG. 7 salt block 21a hasformed therein a recess 72 replicating the shape of the desired toolinsert allowing for the thickness of the protective metal sheath 73.Recess 72 is lined with protective metal 73 (e.g., zirconium) as shownto contain the materials to be made into a composite. Cover salt block21b has recesses therein to accommodate cover sheet 74 completingtheprotective metal enclosure and, preferably, a back-up block ofsintered carbide SC to minimize puncturing of the protective metal layer74. A number of cooperating pairs of salt blocks such as 21a, 21b may beemployed to fill volume 31.

In the tool insert construction 40 of FIG. 3 both faces 41 and 42 of thecemented carbide/abrasive grain composite 43 are formed with a rake(FIG. 4) to facilitate presentation of the CBN cutting edges thereof tothe workpiece.

If desired, most of the tool body 40 may consist of sintered carbide(either preformed or prepared in situ) with only the region forming andadjacent point 44 being of the cemented carbide/abrasive graincomposite. 1

In forming the thin layers 51, 61 of consolidated CBN (about 99 volumepercent) in the tool insert constructions 52, 62 shown in FIGS. 5 and 6,the layer of CBN grains is limited to a maximum thickness of about 0.040inch (1.0 mm) and a minimum thickness of about 0.004 inch (0.1 mm)although the capability exists for preparing such layers in thicknessesas great as about 0.080 inch. The purpose of deliberately making theselayers 51, 61 very thin is in order a). to present the CBN layers 51, 61as chip breaker faces, b). to make it easier to sharpen the tool inserts52, 62 and c). to economize on CBN grit used. Ideally, the relationshipbetween the properties of the CBN layer to the cemented carbide will besuch that the edge of the CBN layer will wear away slightly less rapidlythan the cemented carbide. When this condition prevails, a small amountof the CBN layer will continue to project beyond the face of thecemented carbide body to provide a cutting edge and the amount of CBNutilized will be commensurate with the life of the tool.

After completion of the high temperature, high pressure process, firstthe temperature and then the pressure are reduced. Upon recovery of thetool insert masses, the protective sheath metal remains strongly affixedto the outer surfaces thereof. Exposure of the desired surfaces of thecomposite tool insert is accomplished by simply grinding away theprotective sheath.

It has also been determined that the system is compatible with smallamounts of additive materials, such as tungsten and berylium.

EXAMPLE IV Two sub-assemblies were introduced into (at top and bottom)volume 31 of a high pressure, high temperature apparatus. Eachsub-assembly was enclosed in a Zr cup (0.250 inch diameter) andconsisted of a plug of 883 grade Carboloy sintered carbide (0.050 inchthick) and a mass of 100/120 mesh CBN grains (0.065 g). The CBN grainsin the lower sub-assembly only were coated with a thin layer of Ta metalsputtered thereover. The sub-assemblies were subjected to thesimultaneous application of a pressure of 55 kb and a temperature of1,510C for 60 minutes. The sub-assemblies were recovered, polished andexamined under the microscope.

The upper sub-assembly displayed extensive direct bonding between CBNgrains resulting in a strong abrasive body. There was also excellentadhesion of CBN grains to the sintered carbide.

The lower sub-assembly (Ta-coated CBN) was observed to have many regionsin which CBN grains were sintered together. Other CBN crystals werebonded to the Ta matrix. Good adhesion of the CBN/Ta system to thesintered carbide was evident.

EXAMPLE V A unit was prepared similar to the sub-assemblies of ExampleIV. A Zr cup (0.002 inch Wall thickness and 0.250 inch in diameter)enclosure was loaded with a body (0.5 g) of cold-pressed 883 gradeCarboloy carbide powder and, in contact with the surface thereof, amixture consisting of 400 mesh CBN grains (0.060 g), 883 grade Carboloycarbide powder (0.021 g) and Be powder (0.003 g). The unit ws-subjectedto the simultaneous application of a pressure of 56 kb and a temperatureof 1,520C for 60 minutes. A composite disc was obtained having asintered carbide base (0.070 inch thick) covered on one side with alayer of consolidated CBN (0.028 inch thick) and a uniform diameter of0.232 inch. Strong bonding was observed between CBN grains and sinteredcarbide as well as direct CBN/CBN bonding.

It is to be understood that composites produced as products in thepractice of this invention will, most usually, be bonded to a largerbody, e.g., a tool shank or drill bit for presentation to the materialto be cut.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In a tool insert wherein a unified mass of greater than 70 per centby volume of cubic boron nitride crystals is bonded to a larger metallicmass for support thereof, the combination with said mass of cubic boronnitride crystals of:

a. a single mass of metal bonded carbide directly bonded thereto, saidmass of metal bonded carbide being predominately of carbide materialselected from the group consisting of tungsten carbide, titaniumcarbide, tantalum carbide and mixtures thereof with the metal bondingmaterial therein being selected from the group consisting of cobalt,nickel, iron and mixtures thereof and b. the interface between said massof cubic boron nitride crystals and said metal bonded carbide being freeof voids and being irregular and interlocking on the scale of about1-l00 micrometers, said interlocking occurring between individual cubicboron nitride crystals and portions of the metal bonded carbide mass.

2. The combination of claim 1 wherein the cubic boron nitride content ofthe mass of cubic boron nitride crystals is at least about 99 percent byvolume.

3. The combination of claim 1 wherein the mass of cubic boron nitridecrystals is present as a layer having a thickness of about 0.060 inch orless.

4. A composite abrasive body comprising a mixture of metal bondedcarbide and cubic boron nitride crystals, the metal bonded carbide beingpresent in less than about 30 volume percent.

5. The abrasive body of claim 4 wherein the mixture contains diamondgrains.

6. The process for preparing a composite abrasive body comprising thesteps of:

a. placing within an enclosure of protective metal a quantity of carbidepowder containing metal bonding material therefor and a quantity ofcubic boron nitride crystals, said quantity of carbide powder beingpredominately of carbide material selected from the group consisting oftungsten carbide, titanium carbide, tantalum carbide and mixturesthereof with the metal bonding material therein being selected from thegroup consisting of cobalt, nickel, iron and mixtures thereof,

. simultaneously heating said enclosure and the contents thereof totemperatures in the range of l,300-1,600C and applying pressures theretoin excess of about 40 kilobars for at least 3 minutes,

0. ceasing the input of heat to said enclosure,

(1. removing the pressure applied to said enclosure and e. recoveringthe composite abrasive body produced.

7. The process of claim 6 wherein the carbide powder and cubic boronnitride crystals are two contiguous discrete masses.

8. The process of claim 7 wherein the cubic boron nitride crystals aredisposed in a layer over at least one flat surface of the mass ofcarbide powder, said layer being about 0.060 inch or less in thickness.

9. The process of claim 6 wherein the carbide powder and cubic boronnitride crystals are mixed together, the carbide powder being present inless than about 30 volume percent.

10. The process of claim 6 wherein the carbide powder contains tungstencarbide powder and cobalt powder.

11. The process for preparing a composite abrasive body comprising thesteps of:

a. placing within an enclosure of protective metal a metal bondedcarbide body and contiguous therewith a smaller mass of cubic boronnitride crystals, said metal bonded carbide body being predominately ofcarbide material selected from the group consisting of tungsten carbide,titanium carbide, tantalum carbide and mixtures thereof with the metalbonding material therein being selected from the group consisting ofcobalt, nickel, iron and mixtures thereof, said mass of cubic boronnitride crystals containing greater than about volume percent of cubicboron nitride crystals,

b. simultaneously heating said enclosure and the contents thereof totemperatures in the range of 1,300-l,600C and applying pressures theretoin excess of about 40 kilobars for at least 3 minutes.

balt.

14. The combination of claim 1 wherein the individual cubic boronnitride crystals are larger than about micrometers in largest dimension.

15. The process of claim 6 wherein diamond crystals are also placed withthe protective metal enclosure; the carbide powder, cubic boron nitridecrystals and diamond crystals being mixed together, the carbide powderbeing present in less than about 30 volume percent.

2. The combination of claim 1 wherein the cubic boron nitride content ofthe mass of cubic boron nitride crystals is at least about 99 percent byvolume.
 3. The combination of claim 1 wherein the mass of cubic boronnitride crystals is present as a layer having a thickness of about 0.060inch or less.
 4. A composite abrasive body comprising a mixture of metalbonded carbide and cubic boron nitride crystals, the metal bondedcarbide being present in less than about 30 volume percent.
 5. Theabrasive body of claim 4 wherein the mixture contains diamond grains. 6.The process for preparing a composite abrasive body comprising the stepsof: a. placing within an enclosure of protective metal a quantity ofcarbide powder containing metal bonding material therefor and a quantityof cubic boron nitride crystals, said quantity of carbide powder beingpredominately of carbide material selected from the group consisting oftungsten carbide, titanium carbide, tantalum carbide and mixturesthereof with the metal bonding material therein being selected from thegroup consisting of cobalt, nickel, iron and mixtures thereof, b.simultaneously heating said enclosure and the contents thereof totemperatures in the range of 1,300*-1,600*C and applying pressuresthereto in excess of about 40 kilobars for at least 3 minutes, c.ceasing the input of heat to said enclosure, d. removing the pressureapplied to said enclosure and e. recovering the composite abrasive bodyproduced.
 7. The process of claim 6 wherein the carbide powder and cubicboron nitride crystals are two contiguous discrete masses.
 8. Theprocess of claim 7 wherein the cubic boron nitride crystals are disposedin a layer over at least one flat surface of the mass of carbide powder,said layer being about 0.060 inch or less in thickness.
 9. The processof claim 6 wherein the carbide powder and cubic boron nitride crystalsare mixed together, the carbide powder being present in less than about30 volume percent.
 10. The process of claim 6 wherein the carbide powdercontains tungsten carbide powder and cobalt powder.
 11. The process forpreparing a composite abrasive body comprising the steps of: a. placingwithin an enclosure of protective metal a metal bonded carbide body andcontiguous therewith a smaller mass of cubic boron nitride crystals,said metal bonded carbide body being predominately of carbide materialselected from the group consisting of tungsten carbide, titaniumcarbide, tantalum carbide and mixtures thereof with the metal bondingmaterial therein being selected from the group consisting of cobalt,nickel, iron and mixtures thereof, said mass of cubic boron nitridecrystals containing greateR than about 70 volume percent of cubic boronnitride crystals, b. simultaneously heating said enclosure and thecontents thereof to temperatures in the range of 1,300*-1,600*C andapplying pressures thereto in excess of about 40 kilobars for at least 3minutes, c. ceasing the input of heat to said enclosure, d. removing thepressure applied to said enclosure and e. recovering the compositeabrasive body produced.
 12. The process of claim 11 wherein the cubicboron nitride crystals are disposed in a layer over at least one surfaceof the metal bonded carbide body, said layer being about 0.060 inch orless in thickness.
 13. The process of claim 11 wherein the metal bondedcarbide body contains tungsten carbide and cobalt.
 14. The combinationof claim 1 wherein the individual cubic boron nitride crystals arelarger than about 80 micrometers in largest dimension.
 15. The processof claim 6 wherein diamond crystals are also placed with the protectivemetal enclosure; the carbide powder, cubic boron nitride crystals anddiamond crystals being mixed together, the carbide powder being presentin less than about 30 volume percent.